One could easily imagine lanes controlled by the end user.

For example, "You pay $60 per month for a 50Mbit cable connection consisting of 1 Gigabyte of low latency traffic and unlimited regular traffic". Then the user can set certain programs to be "low latency" using an app available from the cable company. If they want more low-latency traffic, they can pay extra.

Actual implementation through CGNAT could simply involve having different source port ranges for low latency traffic.

Now the key thing is: does traffic not specially marked as "low latency" get artificial latency imposed on it in order to maintain the value of the low latency offering?

You can imagine all sorts of things that would be great, but you have to acknowledge the reality that market forces don't work brilliantly on ISPs in many places.

I feel like this problem only exists in the minds of programmers since in the realm of law you get to take intent into consideration.

What law, though?

That implies a consumer-friendly regulatory regime that can be persuaded to keep up with all the different attempts to game the system. The idea behind net neutrality would be only having to have this fight once to assert that all traffic is of equal value.

Edit: this comment expresses exactly what I want to say already https://news.ycombinator.com/item?id=21762679

> An app available from the cable company That will be filled with spyware and antipatterns.

Software vendor and end user. Not the ISP You pay 20 euro for 70-100 mbit slow lane and pay couple more for the low latency bandwidth that you need.